An electrophoresis display is a non-emissive device based on the electrophoresis phenomenon of charged pigment particles suspended in a solvent. The electrophoresis display usually comprises two plates with electrodes placed opposing each other, separated by using spacers. One of the electrodes is usually transparent. A suspension is enclosed between the two plates. When a voltage difference is imposed between the two electrodes, the pigment particles migrate to one side and then either the color of the pigment or the color of the solvent can be seen according to the polarity of the voltage difference.
PCT International Publication No. WO/2001/067170 discloses an electrophoresis display that includes plural cup-like indentations (cells) created by microembossing or imagewise exposure. The cells are filled with dispersions, which are charged pigment particles, in a dielectric solvent or solvent mixture. A polymer sealing film for sealing the cells filled with the dispersions is formed by curing a sealing composition on top of the dispersions, which sealing composition has a specific gravity lower than the dispersions and is at least partially immiscible with the dispersions.
A problem with this electrophoresis display is that, because microembossing or imagewise exposure is used for creating the cells, it is difficult to reduce the thickness of the cell wall separating the adjacent cells. The thickness of the cell wall affects display properties. The thicker the cell wall, the smaller the display area, resulting in reduced display properties such as lower reflectance and contrast.
The use of microembossing or imagewise exposure for creating the cells also makes it difficult to reduce the thickness of bottom walls of the cells. In the case of microembossing, the cells are formed by embossing a film with a mold and transferring the shape of the mold. The lower limit of the film thickness with this technique is about 100 μm. Accordingly, it is difficult to create cells with a bottom wall thickness of 10 μm or less. In the case of imagewise exposure, the cells are formed in a resist layer deposited on a film, by which film the bottom wall thickness of the cells is defined. With this technique, it is difficult to handle a film with a thickness of 10 μm or less. Accordingly, it is difficult to create cells with a bottom wall thickness of 10 μm or less. It is therefore impossible to reduce a drive voltage required for driving the charged pigment particles filling the cells. In the case where the bottom walls of the cells are used as a display surface, the reflectance is low.
Furthermore, if the thickness of the cell wall separating the adjacent cells and the thickness of the bottom walls of the cells are reduced, the strength against warping and bending is reduced.
It is necessary to seal the cells filled with charged pigment particles with the polymer sealing film in order to prevent the dielectric solvent from being dried. The greater the thickness of the polymer sealing film, the lower the reflectance, resulting in requiring high drive voltage.